The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
CDM Code Division Multiplexing
D2D Device-to-Device
DL Downlink
E-UTRA Evolved Universal Terrestrial Radio Access
eNB, eNodeB Evolved Node B/Base Station in an E-UTRAN System
E-UTRAN Evolved UTRAN (LTE)
FDM Frequency Division Multiplexing
LTE Long Term Evolution
LTE-A Long Term Evolution Advanced
M2M Machine-to-Machine
PDSCH Physical Downlink Shared Channel
PDCCH Physical Downlink Control Channel
PMCH Physical Multicast Channel
PUCCH Physical Uplink Control Channel
PUSCH Physical Uplink Shared Channel
RNTI Radio Network Temporary Identifier
Rx Reception, Receiver
TDM Time Division Multiplexing
Tx Transmission, Transmitter
UE User Equipment
UP Uplink
UTRAN Universal Terrestrial Radio Access Network
D2D communication is a promising application which could be used to improve the resource usage efficiency, reduce the power consumption at both eNB and UE sides, reduce the traffic in cellular networks, and possibly enable some new services in the future. A new study was proposed for D2D in 3GPP TSG-RAN #52 RP-110706, “On the need for a 3GPP study on LTE device-to-device discovery and communication”, Qualcomm Incorporated, plenary, 31 May-3 Jun. 2011.
There are many motivations to introduce the D2D concept, e.g., it may save resources compared with communications via a network, reduce interferences and save power in devices due to low transmit power, shorten end to end delay, etc. But due to existence of the WiFi DIRECT technique which can realize the D2D function, the D2D communication in LTE has to be designed to be more powerful and efficient to compete. Some features expected from the LTE D2D include controlling interference by the eNB and more efficient resource utilization.
These features can be realized by designing an eNB controlled D2D operation, e.g., when a dedicated resource is allocated by the eNB for the D2D operation, and the eNB controls D2D mode configuration. However, if many devices are capable of the D2D operation, using eNB for control pairing and resource allocation for each device will cause a large burden on the eNB signaling. Moreover, in some cases, one user device initially has no desired counterpart to connect to for the D2D operation and it would like to know all the potential users around. In this case, letting the eNB inform other user devices requires accurate position information which may be unavailable. From this point of view, automatic discovery of other devices is desirable.
In order to enable automatic discovery of D2D devices, a dedicated channel may be reserved for that purpose. In this channel, some devices may send a specific signal having a predefined format, and then other devices listening on this channel would know about the existence of the transmitters. This dedicated channel is called the discovery channel and the specific signal is called the discovery signal. A discovery signal design has been discussed, e.g., in Doppler, K.; Ribeiro, C. B.; Kneckt, J., “Advances in D2D communications: Energy Efficient Service and Device Discovery Radio,” Wireless Communication, Vehicular Technology, Information Theory and Aerospace & Electronic Systems Technology (Wireless VITAE), 2011 2nd International Conference on, vol., no., pp. 1-6, Feb. 28 2011-Mar. 3, 2011; R. Larola et al., “Performing Paging in a Wireless Peer-to-Peer Network”, US Patent Application Publication No. 2009/0017843; and J. Li et al., “Paging a Peer in a Peer-to-Peer Communication Network”, US Patent Application Publication No. 2009/0017797.
After device discovery when interested device/devices are found, still further steps may be required before the actual D2D communication can begin between the devices, which include (but are not limited to): obtaining confirmation that the target device/devices accept/accepts the D2D link setup, and getting resources for the D2D operation.
Since the discovery signal from a single transmitter can be detected by multiple receivers, and one device may detect multiple discovery signals, some coordination is needed. Moreover, it is hard if not impossible for a device to transmit its own discovery signal while detecting discovery signals from other devices if resources for discovery signals are in same frequency band. Thus in order to enable devices to be able detect each other, the discovery signal may be, e.g., time division multiplexed, or the discovery resource may be hopped in time during a certain period. For example, in TDM, the device doesn't transmit simultaneously with at least some other devices in every discovery signal transmission occasion within the period. However, TDM will require a large amount of resource and a long time will be needed for one device to detect all potential discovery signals.
Thus, a device capable of the D2D operation may try to send the discovery signal to be detected by other devices, and try to detect discovery signals from further devices to find interested device/devices to pair with. However, letting each device send the discovery signal may require too much resources, and will make the detection period very long considering a large number of devices in the system. Moreover, the required coordination may be complex. Thus, more efficient device discovery signaling and coordination for the D2D communication is needed.